Photocatalyst, production method thereof, component, and device

ABSTRACT

Provided is a photocatalyst including a photocatalyst in which part of calcium ions are substituted with titanium ions, and part of phosphoric acid ions are substituted with metal oxoacid ions in a calcium hydroxyapatite crystal structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2017-100184, filed on May 19,2017, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a photocatalyst, aproduction method of the photocatalyst, a component, and a device.

BACKGROUND

Titanium oxide (TiO₂) is widely known for a photocatalyst as a materialfor environmental remediation. When this material is irradiated withultraviolet rays, electrons of the valence band are excited to theconduction band, and as a result, most of organic materials can becompletely decomposed into carbon dioxide and water because of strongoxidizability of the holes remained in the valence band.

Since the photocatalytic reaction is a surface reaction, a decompositionreaction is not carried out unless a decomposition target is not presenton the surface. Titanium oxide does not have high affinity to organicmaterials. In the case where a decomposition target is not easilyadsorbed on a surface of the titanium oxide, therefore, a reaction speedis slow. In such a case, an adsorbent, such as activated carbon, hasbeen used in combination with titanium oxide in the art, for the purposeof accelerating adsorption (see Akira Fujishima, Kazuhito Hashimoto,Toshiya Watanabe, “Photocleaning revolution,” CMC, 85-87 (1997)). Use ofthe adsorbent in combination with titanium oxide accelerates adsorption,but reduces an area of the titanium oxide contributing to aphotocatalytic reaction and reduces sites irradiated with light.Therefore, the use thereof becomes a factor for lowering decompositionefficiency, which has a trade-off relationship with the adsorptionacceleration effect. Accordingly, it is desirable that a photocatalystitself ideally has high affinity to organic materials.

In 2003, the research group of Wakamura et al. discovered first time inthe world that a material in which Ti was introduced into an apatite(Ca₁₀(PO₄)₆(OH)₂) skeleton by doping (titanium apatite, may be referredto as “Ti-HAp” hereinafter) exhibited photocatalysis upon irradiation ofultraviolet rays (see Japanese Patent Application Laid-Open (JP-A) No.2000-327315, and M. Wakamura, K. Hashimoto, T. Watanabe; “Photocatalysisby Calcium Hydroxyapatite Modified with Ti(IV): Albumin Decompositionand Bactericidal Effect”, Langmuir, 19, 3428-3431 (2003)). It becameclear from the researches that Ti-HAp had a structure that could berepresented by Ca_(10-x)Ti_(x)(PO₄)₆(OH)₂ where part of Ca sites weresubstituted with Ti (see M. Wakamura, K. Hashimoto, T. Watanabe;“Photocatalysis by Calcium Hydroxyapatite Modified with Ti(IV): AlbuminDecomposition and Bactericidal Effect”, Langmuir, 19, 3428-3431 (2003),and M. Tsukada, M. Wakamura, N. Yoshida, T. Watanabe; “Band Gap andPhotocatalytic Properties of Ti-Substituted Hydroxyapatite: Comparisonwith Anatase-TiO₂”, Journal of Molecular Catalysis A: Chemical, 338,18-23 (2011)), and a new level capable of absorbing ultraviolet rays ofabout 340 nm to about 350 nm was formed by Ti-doping to exhibitphotocatalytic reaction (see M. Tsukada, M. Wakamura, N. Yoshida, T.Watanabe; “Band Gap and Photocatalytic Properties of Ti-SubstitutedHydroxyapatite: Comparison with Anatase-TiO₂”, Journal of MolecularCatalysis A: Chemical, 338, 18-23 (2011).).

Since Ti-HAp includes a structure of apatite that is a substance ofhuman bones, Ti-HAp has high affinity to organic materials, such asproteins (K. Kandori, T. Kuroda, M. Wakamura; “Protein AdsorptionBehaviors onto Photocatalytic Ti(IV)-doped Calcium HydroxyapatiteParticles”, Colloids and Surfaces B: Biointerface, 87, 472-479 (2011).and K. Kandori, M. Oketani, M. Wakamura; “Effects of Ti(IV) Substitutionon Protein Adsorption Behaviors of Calcium Hydroxyapatite Particles”,Colloids and Surfaces B: Biointerfaces, 101, 68-73 (2013), and Ti-HAp isan extremely promising photocatalytic material that compensatesdisadvantages of titanium oxide. For the purpose of impartingantibacterial and antivirus properties, particularly, titanium oxide wasoften used in combination with a metal having antibacterial performance,such as Cu and Ag, in the art (see Akira Fujishima, Kazuhito Hashimoto,Toshiya Watanabe, “Photocleaning revolution,” CMC, 15-36 (1997)). Maincomponents of Ti-HAp are apatite and titanium oxide, both of which aresafe to human bodies. Therefore, use of Ti-HAp for antibacterial andantivirus purposes has been increased, and realized as antibacterialprocessing for air cleaners, masks, kitchen products, stationary,carpets, etc. In fact, Ti-HAp exhibits high decomposition activityagainst Escherichia coli, pathogenic bacteria of plants, etc. (seeMasato Wakamura, a doctoral thesis for Graduate School of TokyoInstitute of Technology, “Development and Application of Titanium-dopedHydroxyapatite Photocatalyst,” September, 2014).

SUMMARY

According to one aspect of the present disclosure, a photocatalystincludes a photocatalyst, in which part of calcium ions are substitutedwith titanium ions and part of phosphoric acid ions are substituted withmetal oxoacid ions in a calcium hydroxyapatite crystal structure.

According to one aspect of the present disclosure, a production methodof a photocatalyst includes dipping calcium-titanium hydroxyapatite in aliquid including metal oxoacid ions to obtain a material, and firing theobtained material to obtain a photocatalyst. The calcium-titaniumhydroxyapatite is obtained by substituting part of calcium ions in acalcium hydroxyapatite crystal structure with titanium ions.

According to one aspect of the present disclosure, a component includesthe photocatalyst.

According to one aspect of the present disclosure, a device includes thephotocatalyst.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph depicting a relationship between the ion exchange timeand lattice constants;

FIG. 2A is a graph depicting a relationship between the ion exchangetime and Ca/Ti determined by x-ray photoelectron spectroscopy (XPS);

FIG. 2B is a graph depicting a relationship between the ion exchangetime and Ca/P determined by XPS;

FIG. 2C is a graph depicting a relationship between the ion exchangetime and Ca/Mo determined by XPS;

FIG. 2D is a graph depicting a relationship between the ion exchangetime and Ti/Mo determined by XPS;

FIG. 2E is a graph depicting a relationship between the ion exchangetime and P/Ti determined by XPS;

FIG. 2F is a graph depicting a relationship between the ion exchangetime and P/Mo determined by XPS;

FIG. 3 is a graph depicting the transition of a CO₂ generation amount upto 3 times of the ion exchange time; and

FIG. 4 is a graph depicting a relationship between the ion exchange timeand a CO₂ generation amount per unit time.

DESCRIPTION OF EMBODIMENTS

The photocatalytic activity of Ti-HAp is determined by a doping amountof Ti. In order to maintain a structure of apatite, the upper limit ofthe doping amount is roughly about 15% of Ca (see M. Tsukada, M.Wakamura, N. Yoshida, T. Watanabe; “Band Gap and PhotocatalyticProperties of Ti-Substituted Hydroxyapatite: Comparison withAnatase-TiO₂”, Journal of Molecular Catalysis A; Chemical, 338, 18-23(2011)). Therefore, oxidizability of Ti-HAp itself is low compared totitanium oxide a crystal of which has a TiO₆ octahedral skeleton.Accordingly, high photocatalytic activity of Ti-HAp is owing toexcellent adsorption power, which apatite originally has, to organicmaterials.

If oxidizability of Ti-HAp can be enhanced significantly, therefore, itis expected that a range of applications of Ti-HAp can be furtherwidened. So far, in association with improvements of the activity ofTi-HAp upon irradiation of ultraviolet rays, a technology for bearing Cuclusters has been reported [see M. Nishikawa, W. Yang, Y. Nosaka, J.Molecular Catal A, 378, 314-318 (2013)]. However, the improvement of theactivity remains about twice the activity of Ti-HAp bearing no Cuclusters.

The present disclosure has an object to provide a photocatalyst havingexcellent photocatalytic activity, a production method of thephotocatalyst, and a component and device using the photocatalyst.

In one aspect of the present disclosure, a photocatalyst havingexcellent photocatalytic activity can be provided.

In one aspect of the present disclosure, moreover, a production methodof a photocatalyst having excellent photocatalytic activity can beprovided.

In one aspect of the present disclosure, moreover, a component includinga photocatalyst having excellent photocatalytic activity can beprovided.

In one aspect of the present disclosure, moreover, a device including aphotocatalyst having excellent photocatalytic activity can be provided.

Photocatalyst

The disclosed photocatalyst is a photocatalyst, in which part of calciumions are substituted with titanium ions and part of phosphoric acid ionsare substituted with metal oxoacid ions in a calcium hydroxyapatitecrystal structure.

In the photocatalyst, an amount of the titanium ions relative to thecalcium ions is not particularly limited and may be appropriatelyselected depending on the intended purpose. In view of maintenance ofthe crystal structure of the apatite, the amount is preferably 20 mol %or less, more preferably 19 mol % or less, and particularly preferably18 mol % or less.

The lower limit of the amount of the titanium ions relative to thecalcium ions is not particularly limited and may be appropriatelyselected depending on the intended purpose. The lower limit ispreferably 0.1 mol % or greater, more preferably 5 mol % or greater,even more preferably 10 mol % or greater, and particularly preferably 13mol % or greater.

The metal oxoacid ion is an oxoacid anion of a transition metal element.

A metal included in the metal oxoacid ion is a transition metal.

Examples of the transition metal include tungsten (W), manganese (Mn),molybdenum (Mo), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), and rhenium (Re). The above-listed examples may be used alone orin combination.

Examples of the metal oxoacid ions include tungstate ions, manganateions, molybdate ions, vanadate ions, tungstomolybdate ions,vanadomolybdate ions, vanadotungstate ions, manganese tungstate ions,cobalt tungstate ions, silicotungstate ions, and manganese molybdenumtungstate ions. Among the above-listed examples, molybdate ions (MoO₄²⁻), manganate ions (MnO₄ ⁻), and vanadate ions (VO₄ ³⁻) are preferable.

The above-listed examples are used alone or in combination.

An amount of the metal oxoacid ions relative to the phosphoric acid ionsin the photocatalyst is not particularly limited and may beappropriately selected depending on the intended purpose. The amount ispreferably 0.1 mol % or greater but 5.0 mol % or less, more preferably0.5 mol % or greater but 3.0 mol % or less, and particularly preferably1.0 mol % or greater but 2.0 mol % or less.

Shape Etc. Of Photocatalyst

A shape, structure, and size of the photocatalyst are not particularlylimited and may be appropriately selected depending on the intendedpurpose.

Examples of the shape include powderous shapes, granular shapes, tabletshapes, rod shapes, plate shapes, block shapes, sheet shapes, and filmshapes. Among the above-listed examples, powderous shapes (powder) arepreferable in view of handling.

Examples of the structure include needle structures, plate structures,dendritic structures, corrugated sheet structures, relief structures,single-layer structures, laminate structures, porous structures, andcore-shell structures.

Note that, determination of the photocatalyst and observation of theform etc. of the photocatalyst can be performed, for example, by meansof a transmission electron microscope (TEM), an X-ray diffraction (XRD)device, an X-ray photoelectron spectrometer (XPS), a Fourier transforminfrared (FT-IR) spectrometer, an inductively coupled plasma-atomicemission spectrometer (ICP-AES), an X-ray fluorescence (XRF)spectrometer, etc.

Embodiment of Use

The photocatalyst may be used per se, or may be used in combination withanother material, or may be used in the state of a slurry by dispersingthe photocatalyst in a liquid substance, such as water, andalcohol-based solvents. In the case where the photocatalyst is used inthe form of the slurry, the liquid is preferably water. The resultantslurry can be suitably used as a slurry including a photocatalyst.

The photocatalyst may be used per se, or may be used as a mixedcomposition by grinding and mixing the photocatalyst with anothercomposition etc., or may be used by forming the photocatalyst into afilm (surface coating film) on a base through deposition or coating. Inthe case where the photocatalyst is deposited or coated on a base etc.,a coating liquid is suitably used.

A method of the grinding is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe method include methods where grinding is performed using a ball milletc.

The above-mentioned another composition is not particularly limited andmay be appropriately selected depending on the intended purpose.Examples of the composition include printing inks.

A method of the mixing is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe method include methods using kneaders, stirrers, etc.

A material, shape, structure, and thickness of the base are notparticularly limited and may be appropriately selected depending on theintended purpose. Examples of the material of the base include paper,synthetic paper, woven fabrics, non-woven fabrics, leather, wood, glass,metals, ceramics, and synthetic resins. Examples of the shape of thebase include foil shapes, film shapes, sheet shapes, and plate shapes.

A method of the deposition is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe method include spraying.

A method of the coating is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe method include spray coating, curtain coating, spin coating, gravurecoating, inkjet, and dipping.

The coating liquid is not particularly limited and may be appropriatelyselected depending on the intended purpose, as long as the coatingliquid includes the photocatalyst. Examples of the coating liquidinclude a coating liquid obtained by adding an alcohol solution, whichis prepared by adding the photocatalyst into isopropyl alcohol etc., toan inorganic coating liquid material etc., and mixing the resultantmixture. The inorganic coating liquid material is not particularlylimited and may be appropriately selected depending on the intendedpurpose. Examples of the inorganic coating liquid material include acold setting inorganic coating agent (an agent obtained by mixing aliquid material of the product name, S00 and a liquid material ofproduct name, UTE01, both available from Nihon Yamamura Glass Co., Ltd.,at a mass ratio of 10:1).

Applications Etc.

The photocatalyst can be used for various applications of photocatalystsknown in the art.

The photocatalyst can be suitably used in various fields. Specifically,the photocatalyst can be suitably used for OA devices (e.g., housings ofcomputers, mouse, and keyboards), electronic devices (e.g., phones,photocopiers, facsimiles, various printers, digital cameras, videocassette recorders and players, CD recorders and players, DVD recordersand players, air conditioners, and remote controllable devices),electric appliances (e.g., dish washers, dish driers, tumble driers,washing machines, air cleaners, humidifiers, fans, extractor fans,vacuum cleaners, and kitchen waste disposal devices), mobile informationterminals (e.g., PDA, mobile phones, and smart phones), filters (filtersfor gas: filters used for air cleaners, air conditioners, etc., filtersfor liquids: filters for hydroponic liquid treatments etc., filters forsolids: filters for soil improvements etc., and filters for cameras),wall paper, food containers (e.g., reusable containers and disposalcontainers), medical devices and hygiene products (e.g., mask parts ofoxygen inhalers, bandages, masks, and antibacterial gloves), textileproducts, such as clothes, dentures, interior and exterior materials(e.g., interior and exterior materials formed of resins, paper, cloth,ceramics, metals etc.; materials for bath, swimming pools, andbuildings; and materials for medical facilities, bio experiment rooms,and clean benches, which apply light of a fluorescent lamp at the timeof use by users, and apply ultraviolet rays when it is not used byusers), vehicles (e.g., materials for interiors, and mirrors of vehiclesfor checking rear views), straps (e.g., straps for trains and buses),steering wheels and handles (steering wheels and handles for bicycles,tricycles, motor cycles, and automobiles), saddles (e.g., saddles forbicycles, tricycles, and motor cycles), shoes (e.g., shoes made ofcloth, resins, artificial leather, and synthetic resins), bags (e.g.,bags made of cloth, resins, artificial leather, and synthetic resins),coating materials (e.g., coating films), sewage and waste water treatingmaterials (e.g., a material, in which a photocatalyst having absorbanceto light of a wide range is blended in porous silica), a sheet (e.g., asoil treatment sheet), electrodes of biochips (e.g., electrodes incombination with organic dyes), mirrors (e.g., mirrors for bathrooms,mirrors for lavatory, dental mirrors, and road mirrors), lenses (e.g.,spectacle lenses, optical lenses, lenses for lighting, lenses forsemiconductor devices, lenses for photocopiers, and lenses for rear viewcameras for vehicles), prisms, glass (e.g., window glass for buildingsor watchtowers; window glass for vehicles, such as automobile, trains,aircrafts, ships, submersible, snowmobile, ropeway gondolas, gondolasfor amusement parks, and spaceship; windshield glass for vehicles, suchas automobile, trains, aircrafts, ship, submersible, snowmobile, ropewaygondolas, gondolas for amusement parks, and spaceship; glass of displaycases for frozen food, and glass of display cases for heated food, suchas Chinese steamed bun), goggles (e.g., protective goggles, and sportsgoggles), shields (e.g., shields for protective masks, shields forsports masks, and shields of helmets), covers (e.g., covers formeasuring equipment, and covers of rear view cameras for automobiles),lenses (e.g., focusing lenses, such as for laser dental equipment),covers (e.g., covers of laser photodetecting sensors, such as afollowing distance sensors, covers of infrared sensors, films, sheets,stickers, and emblems).

A production method of the photocatalyst is not particularly limited andmay be appropriately selected depending on the intended purpose. Thephotocatalyst is preferably produced by the production method describedbelow.

Production Method of Photocatalyst

The disclosed production method of a photocatalyst includes at least adipping and firing step, preferably further includes a repeating step,and may further include other steps according to the necessity.

The production method of a photocatalyst is suitable as a productionmethod of the disclosed photocatalyst.

Dipping and Firing Step

The dipping and firing step is not particularly limited and may beappropriately selected depending on the intended purpose, as long as thedipping and firing step is a step including dipping calcium-titaniumhydroxyapatite in a liquid including metal oxoacid ions to obtain amaterial and firing the obtained material.

Calcium-Titanium Hydroxyapatite

The calcium-titanium hydroxyapatite is a material in a state where partof calcium ions in a calcium hydroxyapatite crystal structure aresubstituted with titanium ions.

Examples of the calcium-titanium hydroxyapatite include Ca₉Ti(PO₄)₆(OH)₂and Ca₈Ti(PO₄)₆(OH)₂.

The calcium-titanium hydroxyapatite may be synthesized or selected fromcommercial products. For example, the commercial products are readilyavailable from Fuji Chemical Industries Co., Ltd. and TAIHEI CHEMICALINDUSTRIAL CO., LTD.

In the calcium-titanium hydroxyapatite, an amount of the titanium ionsrelative to the calcium ions is not particularly limited and may beappropriately selected depending on the intended purpose. In view ofmaintenance of the crystal structure of the apatite, the amount ispreferably 20 mol % or less, more preferably 19 mol % or less, andparticularly preferably 18 mol % or less.

In the calcium-titanium hydroxyapatite, the lower limit of the amount ofthe titanium ions relative to the calcium ions is not particularlylimited and may be appropriately selected depending on the intendedpurpose. The lower limit is preferably 0.1 mol % or greater, morepreferably 5 mol % or greater, even more preferably 10 mol % or greater,and particularly preferably 13 mol % or greater.

Liquid

The liquid includes metal oxoacid ions. Examples of the liquid includeaqueous solutions.

Metal Oxoacid Ion

The metal oxoacid ion is an oxoacid anion of a transition metal element.

A metal included in the metal oxoacid ion is a transition metal.

Examples of the transition metal include tungsten (W), manganese (Mn),molybdenum (Mo), vanadium (V), niobium (Nb), tantalum (Ta), chromium(Cr), and rhenium (Re). The above-listed examples may be used alone orin combination.

Examples of the metal oxoacid ions include tungstate ions, manganateions, molybdate ions, vanadate ions, tungstomolybdate ions,vanadomolybdate ions, vanadotungstate ions, manganese tungstate ions,cobalt tungstate ions, silicotungstate ions, and manganese molybdenumtungstate ions. Among the above-listed examples, molybdate ions (MoO₄²⁻), manganate ions (MnO₄ ⁻), and vanadate ions (VO₄ ³⁻) are preferable.

The above-listed examples may be used alone or in combination.

The liquid is obtained by dissolving a metal oxoacid salt in water.

A cation of the metal oxoacid salt is not particularly limited and maybe appropriately selected depending on the intended purpose. Examples ofthe cation include alkaline earth metals, and alkali metals.

An amount of the metal oxoacid ions in the liquid is not particularlylimited and may be appropriately selected depending on the intendedpurpose. The amount is preferably 0.01 mol/L or greater but 1 mol/L orless, and more preferably 0.05 mol/L or greater but 0.5 mol/L or less.

Dipping

A temperature of the liquid at the time of the dipping is notparticularly limited and may be appropriately selected depending on theintended purpose. The temperature is preferably 20° C. or higher but 50°C. or lower, and more preferably 20° C. or higher but 30° C. or lower.

At the time of the dipping, the liquid is preferably stirred to turn theliquid into a suspension.

Duration of the dipping is not particularly limited and may beappropriately selected depending on the intended purpose. The durationis preferably 1 minute or longer but 1 hour or shorter.

A material obtained by the dipping may be washed and dried after thedipping but before the firing. Methods of the washing and the drying arenot particularly limited and may be appropriately selected depending onthe intended purpose.

Firing

A temperature of the firing is not particularly limited and may beappropriately selected depending on the intended purpose. Thetemperature is preferably 200° C. or higher but 600° C. or lower, andmore preferably 400° C. or higher but 550° C. or lower.

Duration of the firing is not particularly limited and may beappropriately selected depending on the intended purpose. The durationis preferably 10 minutes or longer but 2 hours or shorter.

Repeating Step

The repeating step is not particularly limited and may be appropriatelyselected depending on the intended purpose, as long as the repeatingstep includes performing a step once or a plurality of times, where thestep includes dipping the photocatalyst obtained from the dipping andfiring step in a liquid including metal oxoacid ions to obtain amaterial and firing the obtained material. The step is preferablyperformed once to 4 times.

As conditions for the dipping and the firing, the conditions of thedipping and the conditions of the firing in the dipping and firing stepare listed as examples.

A substitution amount of the metal oxoacid ions in the calcium-titaniumhydroxyapatite can be increased by performing the dipping and the firingseveral times.

Component

The disclosed component includes the disclosed photocatalyst.

Within the component, the photocatalyst is, for example, formed into afilm that constitutes part of the component.

Examples of the component include housings (e.g., housings of electroniccomponents, electronic devices, electric appliances, and mobileinformation terminals), filters, wall paper, components of medicaldevices and hygiene products, lenses, prisms, and glass.

Device

The disclosed device includes the disclosed photocatalyst.

Within the device, the photocatalyst is, for example, arranged on asurface of housing of the device to constitute part of the device.

Examples of the device include OA devices (e.g., computers, tablets,mouse, and keyboards), vehicles (e.g., bicycles, automobiles, andtrains), electronic devices (e.g., phones, photocopiers, facsimiles,various printers, digital cameras, video cassette recorders and players,CD recorders and players, DVD recorders and players, air conditioners,and remote controllable devices), electric appliances (e.g., dishwashers, dish driers, tumble driers, washing machines, air cleaners,humidifiers, fans, extractor fans, vacuum cleaners, and kitchen wastedisposal devices), and mobile information terminals (e.g., PDA, mobilephones, and smart phones).

EXAMPLES

The disclosed photocatalyst will be concretely described throughexamples hereinafter, but these examples shall not be construed as tolimit a scope of the disclosed photocatalyst in any way.

In Examples below, each analysis was performed in the following manner.

Measurement of Lattice Constants [XRD]

Analysis device: XRD-6100 available from Shimadzu CorporationAccelerating voltage: 40 kVX-ray source: Cu

Surface Chemical Composition Analysis [XPS]

Analysis device: ESCA 5500MT; Perkin Elmer Inc., U.S.A.Accelerating voltage: 14 kVX-ray source: Al Kα (1486.6 eV)

Bulk Chemical Composition Analysis [ICP Analysis]

Analysis device: 5100 VDV ICP-OES (Agilent Technologies)Treatment of samples: Wet decomposition was performed with mixed acidsof sulfuric acid, nitric acid, and hydrochloric acid for 9 hours.

Example 1 Production of Photocatalyst

In 200 mL of a CaMoO₄ aqueous solution (concentration: 0.1 mM), 1 g ofcommercially available Ti-HAp powder (available from Fuji ChemicalIndustries Co., Ltd.) including about 10 mol % of Ti relative to anamount of Ca was suspended for 5 minutes, and the resultant wasfiltered, washed, and dried, followed by firing the resultant for 1 hourat 500° C. in the atmosphere. The aforementioned process from thesuspending through the firing was further performed on the resultantonce to 7 times. As a result, photocatalyst powder samples whose ionexchange time was respectively once to 8 times were obtained.

Analysis

A specific surface area of any of the obtained powder samples was from35 m²/g to 40 m²/g, and the crystal phase was an apatite single phase.However, the lattice constants of the appatite crystal (FIG. 1) and thesurface chemical composition (FIGS. 2A to 2F) were changed by repeatingthe suspension through firing process. Since the lattice constants werechanged, it was suggested that a certain amount of a materialsubstitution occurred within the structure. It became clear from thechange in the chemical composition that mainly PO₄ ³⁻ was substitutedwith MoO₄ ²⁻ during the first 5 repetitions of the process. No changewas observed in the visible-ultraviolet ray absorption spectra of thesamples.

It is assumed from the results above and the ICP analysis results that ageneral formula of the obtained photocatalyst is as follows.

(Ca_(10-2x)Ti_(x−(y/4)),▴_(x+(y/4))(PO₄)_(6−y)(MoO₄)_(y)(OH)₂

For example, 1.10≤x≤1.30, and 0<y≤0.100.

In the general formula above, ▴ denotes a void.

Moreover, relationships between the number of the times dipping andfiring was performed (ion exchange time) and compositions of theobtained photocatalysts are as follows according to the XPS analysisresults and the ICP analysis results.

TABLE 1 Ion exchange time (times) Chemical composition 0 (Ca_(7.37),Ti_(1.31), ▴_(1.31))(PO₄)₆(OH)₂ 1 (Ca_(7.41), Ti_(1.26),▴_(1.29))(PO₄)_(5.922)(MoO₄)_(0.078)(OH)₂ 2 (Ca_(7.51), Ti_(1.21),▴_(1.25))(PO₄)_(5.919)(MoO₄)_(0.081)(OH)₂ 3 (Ca_(7.58), Ti_(1.17),▴_(1.21))(PO₄)_(5.911)(MoO₄)_(0.089)(OH)₂ 4 (Ca_(7.62), Ti_(1.14),▴_(1.19))(PO₄)_(5.909)(MoO₄)_(0.091)(OH)₂ 5 (Ca_(7.64), Ti_(1.13),▴_(1.18))(PO₄)_(5.91)(MoO₄)_(0.09)(OH)₂

Photocatalytic Activity

The obtained powder was collected by 40 mg. The collected powder washomogeneously dispersed in a region of 8.35 cm² to thereby obtain asample. The sample was set in a 500 mL glass container, and ultravioletrays (wavelength: 365 nm) having intensity of 1 mW/cm² was applied usinga Hg—Xe lamp with adding isopropyl alcohol vapor in a manner that a gasphase concentration was to be 700 ppm. The gas inside the container wascollected per certain period of time, and a concentration of CO₂ gasgenerated by decomposition of isopropyl alcohol was quantified by gaschromatography. The CO₂ generation amount per unit time (ppm/h) wascalculated from the CO₂ generation amount measured from the start oflight irradiation to 6 hours later.

The analysis results are presented in FIGS. 3 and 4. FIG. 3 is a graphdepicting the transition of the CO₂ generation amount from the start tothe repeating number (ion exchange time) of 3 times. FIG. 4 is a graphdepicting a relationship between the ion exchange time and the CO₂generation amount per unit time. FIG. 4 presents an average valueobtained from the values obtained by measuring several times. The CO₂generation rate increased along with the increase of the number of theion exchange performed by the CaMoO₄ aqueous solution, and was almostsaturated when the ion exchange was performed about 5 times. At the timeof saturation, the CO₂ generation amount was about 140 ppm/h.

Example 2 Production of Photocatalyst

Samples were produced in the same manner as in Example 1, except that200 mL of the CaMoO₄ aqueous solution (concentration: 0.1 mM) wasreplaced with 200 mL of a KMnO₄ aqueous solution (concentration: 0.1mM).

Analysis

A specific surface area of any of the obtained powder samples was from35 m²/g to 40 m²/g, and the crystal phase of each of the powder sampleswas an apatite single phase. No change was obtained in thevisible-ultraviolet ray absorption spectra of the samples.

Photocatalytic Activity

Photocatalytic activity was evaluated in the same manner as inExample 1. The CO₂ generation rate was 48 ppm/h when the treatment withthe KMnO₄ aqueous solution was performed once.

Example 3 Production of Photocatalyst

Samples were produced in the same manner as in Example 1, except that200 mL of the CaMoO₄ aqueous solution (concentration: 0.1 mM) wasreplaced with 200 mL of a Na₃VO₄ aqueous solution (concentration: 0.1mM).

Analysis

A specific surface area of any of the obtained powder samples was from35 m²/g to 40 m²/g, and the crystal phase of each of the powder sampleswas an apatite single phase. No change was obtained in thevisible-ultraviolet ray absorption spectra of the samples.

Photocatalytic Activity

An evaluation of photocatalytic activity was performed in the samemanner as in Example 1. The CO₂ generation rate when the treatment withthe Na₃VO₄ aqueous solution was performed once was 133 ppm/h. When theK₃VO₄ aqueous solution was used, moreover, the CO₂ generation rate was122 ppm/h, which was the similar value.

Comparative Example 1 Photocatalytic Activity

Photocatalytic activity of the commercially available Ti-HAp powder usedin Example 1 was evaluated in the same manner as in Example 1. The CO₂generation rate was about 14 ppm/h.

It was confirmed from Examples and Comparative Example above thatExamples could effectively decompose and remove organic materials usinga material in which Ti was introduced into the apatite (e.g.,Ca₁₀(PO₄)₆(OH)₂) skeleton through substitution, where phosphoric acidions therein were substituted with metal oxoacid ions. It was confirmedfrom the results above that a significant improvement in activity couldbe realized compared to Ti-HAp known in the art.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the sprit and scope of the invention.

What is claimed is:
 1. A photocatalyst comprising: a photocatalyst inwhich part of calcium ions are substituted with titanium ions, and partof phosphoric acid ions are substituted with metal oxoacid ions in acalcium hydroxyapatite crystal structure.
 2. The photocatalyst accordingto claim 1, wherein an amount of the titanium ions relative to thecalcium ions is 0.1 mol % or greater but 20 mol % or less.
 3. Thephotocatalyst according to claim 1, wherein an amount of the titaniumions relative to the calcium ions is 10 mol % or greater but 19 mol % orless.
 4. The photocatalyst according to claim 1, wherein an amount ofthe titanium ions relative to the calcium ions is 13 mol % or greaterbut 18 mol % or less.
 5. The photocatalyst according to claim 1, whereinthe metal oxoacid ions are at least one of tungstate ions, manganateions, molybdate ions, vanadate ions, tungstomolybdate ions,vanadomolybdate ions, vanadotungstate ions, manganese tungstate ions,cobalt tungstate ions, silicotungstate ions, and manganese molybdenumtungstate ions.
 6. The photocatalyst according to claim 1, wherein themetal oxoacid ions are at least one of molybdate ions, manganate ions,and vanadate ions.
 7. The photocatalyst according to claim 1, wherein anamount of the metal oxoacid ions relative to the phosphoric acid ions is0.1 mol % or greater but 5.0 mol % or less.
 8. The photocatalystaccording to claim 1, wherein an amount of the metal oxoacid ionsrelative to the phosphoric acid ions is 1.0 mol % or greater but 2.0 mol% or less.
 9. A production method of a photocatalyst, the methodcomprising: dipping calcium-titanium hydroxyapatite in a liquidincluding metal oxoacid ions to obtain a material, where thecalcium-titanium hydroxyapatite is obtained by substituting part ofcalcium ions in a calcium hydroxyapatite crystal structure with titaniumions; and firing the obtained material to obtain a photocatalyst. 10.The production method according to claim 9, further comprising:performing a step once or a plurality of times, where the step includesdipping the obtained photocatalyst in a liquid including metal oxoacidions to obtain a material and firing the obtained material.
 11. Theproduction method according to claim 9, wherein the metal oxoacid ionsare at least one of molybdate ions, manganate ions, and vanadate ions.12. A device comprising: a photocatalyst, wherein the photocatalyst is aphotocatalyst in which part of calcium ions are substituted withtitanium ions, and part of phosphoric acid ions are substituted withmetal oxoacid ions in a calcium hydroxyapatite crystal structure.